As good an answer as any to the question:
"Why do seemingly regular people go crazy and decide to kill others?"
Chorus, from the song:
Tell me why?
I don't like Mondays!
Tell me, why?
I don't like Mondays!
Tell me, why, oh why, I shot the whole day down.
Ironic trivia: Bob Geldolf, who wrote this song, later became famous/infamous for the Live Aid concert and the terrible "We Are The World" song.
So his depressing song is remembered as funny and his uplifting song is remembered as sugary pap.